HV823
External Component Description
External Component
Diode
Cs Capacitor
R
EL-osc
Selection Guide Line
Fast reverse recovery diode, 1N4148 or equivalent.
0.01µF to 0.1µF, 100V capacitor to GND is used to store the energy transferred from the inductor.
The EL lamp frequency is controlled via an external R
EL
resistor connected between R
EL-osc
and V
DD
of the
device. The lamp frequency increases as R
EL
decreases. As the EL lamp frequency increases, the amount
of current drawn from the battery will increase and the output voltage V
CS
will decrease. The color of the EL
lamp is dependent upon its frequency.
A 2MΩ resistor would provide lamp frequency of 330 to 450Hz. Decreasing the R
EL-osc
by a factor of 2 will
increase the lamp frequency by a factor of 2.
R
SW-osc
The switching frequency of the converter is controlled via an external resistor, R
SW
between R
SW-osc
and V
DD
of the device. The switching frequency increases as R
SW
decreases. With a given inductor, as the switching
frequency increases, the amount of current drawn from the battery will decrease and the output voltage, V
CS
,
will also decrease.
A 1nF capacitor is recommended on R
SW-osc
to GND when a 0.01µF C
S
capacitor is used. This capacitor
is used to shunt any switching noise that may couple into the R
SW-osc
pin. The C
SW
capacitor may also be
needed when driving large EL lamp due to increase in switching noise.
The inductor L
x
is used to boost the low input voltage by inductive flyback. When the internal switch is on,
the inductor is being charged. When the internal switch is off, the charge stored in the inductor will be
transferred to the high voltage capacitor C
S
. The energy stored in the capacitor is connected to the internal
H-bridge and therefore to the EL lamp. In general, smaller value inductors, which can handle more current,
are more suitable to drive larger size lamps. As the inductor value decreases, the switching frequency of the
inductor (controlled by R
SW
) should be increased to avoid saturation.
560µH Murata inductors with 14.5Ω series DC resistance is typically recommended. For inductors with the
same inductance value but with lower series DC resistance, lower R
SW
value is needed to prevent high current
draw and inductor saturation.
Lamp
As the EL lamp size increases, more current will be drawn from the battery to maintain high voltage across
the EL lamp. The input power, (V
IN
x I
IN
), will also increase. If the input power is greater than the power
dissipation of the package (400mW), an external resistor in series with one side of the lamp is recommended
to help reduce the package power dissipation.
C
SW
Capacitor
Lx Inductor
Enable/Disable Configuration
The HV823 can be easily enabled and disabled via a logic control
signal on the R
SW
and R
EL
resistors as shown in Figure 4 below.
The control signal can be from a microprocessor. R
SW
and R
EL
are typically very high values. Therefore, only 10’s of microam-
peres will be drawn from the logic signal when it is at a logic high
(enable) state. When the microprocessor signal is high the
device is enabled and when the signal is low, it is disabled.
Figure 4: Enable/Disable Configuration
ON =V
DD
OFF = 0V
Remote
Enable
R
EL
1
R
SW
L
x
+
V
IN
= V
DD
-
4.7µF
15V
V
DD
R
SW-osc
C
s
L
x
R
EL-osc
V
A
V
B
GND
8
7
EL Lamp
2
3
1N4148
6
5
4
C
S
100V
HV823LG
1nF
7
SUPERTEX [ Supertex, Inc ]
